Apparatus, and associated method, for communicating a data block in a multi carrier modulation communication scheme

ABSTRACT

Apparatus, and an associated method, for sending a data block in an OFDM, or other MCM, communication system with reduced PAPR is provided. The data block is combined with a random scrambling sequence. An IDFT operation is performed upon the combined sequence, and its PAPR, peak-to-average power ratio, is calculated. The PAPR is compared against a threshold. If the PAPR is smaller than a threshold, the transformed, combination sequence is transmitted. Otherwise, a different scrambling sequence, if available, is used to form a new combination sequence, and the process iterates until either a PAPR smaller than the threshold is obtained, or a pre-defined maximum number of iterations is reached. If the maximum number of iterations is reached and no combination sequence is created that leads to an acceptable PAPR, then the transformed, combination sequence that exhibits the smallest PAPR level is selected for transmission.

The present invention relates generally to a manner by which tocommunicate a data block in an OFDM-based or other MCM-basedcommunication system. More particularly, the present invention relatesto apparatus, and an associated method, by which to combine the datablock with a randomized, scrambling sequence to form a combinationsequence that leads to a PAPR (Peak-to-Average Power Ratio) of selectedcharacteristics.

The data block is combined with successive scrambling sequences until acombination sequence is formed that leads to the PAPR of selectedcharacteristics. And, the combination sequence that leads to theseselected characteristics is transmitted. If none of the combinationsequences leads to a PAPR of the selected characteristics, then thecombination sequence that leads to the smallest PAPR is transmitted.Through random or appropriate selection of the combination sequence, theinformational content of the data block is communicated while avoidingproblems that sometimes result when transmitting data blocks that leadto high PAPRs.

BACKGROUND OF THE INVENTION

The use of radio communication systems through which to communicate ispervasive in modern society. Cellular communication systems, forinstance, are deployed throughout significant portions of the populatedareas of the world, providing users access to communicate therethroughwhen positioned in an area encompassed by a cellular communicationsystem. Successive generations of cellular communication systems havebeen developed and deployed, each successive generation providingincreased communication capabilities. For instance, whileearly-generation cellular communication systems were used primarily forvoice communications, successor-generation cellular communicationsystems provide increased data communication capabilities.New-generation systems are capable of providing multimedia communicationservices at guaranteed levels of quality.

In a cellular communication system, and more generally, any radio, aswell as another, communication system, channel bandwidth allocation islimited. The frequency spectrum allocated for use by a cellularcommunication system is limited, and such limitation is regularly alimiting factor in the communication capacity of the system. Effort ismade, therefore, to utilize the allocated capacity in an efficientmanner.

OFDM (Orthogonal Frequency Division Multiplexing) schemes, and other MCM(Multi-Carrier Modulation) schemes, e.g., provide the possibility ofmore efficient usage of channel bandwidth, thereby permitting increasedspeed for data to be communicated within a given channel bandwidth. Inan OFDM communication scheme, sub-carriers are defined that areorthogonal. In an OFDM scheme, power management is an importantfunction. Power efficiency, e.g., is, dependent upon powercharacteristics of communications upon OFDM-defined channels. One powercharacteristic of interest is a PAPR, Peak-To-Average Power Ratio. It isgenerally desired to communicate data at a relatively low PAPR. When thedata leads to a higher PAPR, the power amplifier (PA) at a transmitstation has to operate at a lower level of average power. When operatedat the lower average power level, the resultant signal is of lowertransmit power, and the coverage area of service is reduced. And, whenoperated at the lower average power level, the PA operates with a lowerpower efficiency, resulting in a higher service cost, and reducedbattery longevity if the transmit station is powered by a battery powersupply.

If a manner could be provided by which better to ensure that data thatis to be communicated in an OFDM, or other MCM, communication systemleads to an acceptably low PAPR level, communication improvements wouldbe likely.

It is in light of this background information related to communicationsin an OFDM or MCM communication scheme that significant improvements ofthe present invention have evolved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a functional block diagram of a radio communicationsystem in which an embodiment of the present invention is operable.

FIG. 2 illustrates a process diagram representative of the process ofoperation of an embodiment of the present invention.

FIG. 3 illustrates a method flow diagram representative of the method ofoperation of an embodiment of the present invention.

DETAILED DESCRIPTION

The present invention, accordingly, advantageously provides apparatus,and an associated method, for communicating a data block in anOFDM-based, or other MCM-based, communication system.

Through operation of an embodiment of the present invention, a manner isprovided by which to combine the data block with a randomized,scrambling sequence to form a combination sequence that leads to a PAPR(Peak-to-Average Power Ratio) of selected characteristics.

In one aspect of the present invention, the data block is combined withsuccessive scrambling sequences until a combination sequence is formedthat leads to the PAPR of the selected characteristics. Once thecombination sequence that leads to the PAPR of the selectedcharacteristics is formed, the combination sequence is transmitted.

In another aspect of the present invention, if none of the combinationsequences leads to a PAPR of the selected characteristics, then acombination sequence that leads to the smallest PAPR is selected fortransmission.

Through selection of the combination sequence that leads to a PAPR ofselected characteristics, or a smallest-available PAPR level, theinformational content of the data block is communicated while reducingthe likelihood of occurrence of problems that sometimes result when datablocks leading to high PAPRs are transmitted.

In another aspect of the present invention, a product sequence is formedof a data block that is to be communicated multiplied with a binarysequence. Once formed, an inverse discrete Fourier transform (IDFT) isperformed upon the product sequence and the PAPR after IDFT iscalculated. If the calculated PAPR is smaller than a pre-definedthreshold, then the product sequence is caused for transmission.

If, conversely, the calculated PAPR of the product sequence after IDFTis not smaller than the threshold level, then the PAPR level and thetransformed product sequence are buffered, and a new product sequence isformed, formed of another scrambling sequence multiplied with the datablock. An iterative procedure of performing an IDFT on the newly createdproduct sequence, calculation of the PAPR, and comparison with thethreshold value is performed. The iterative procedure continues until aPAPR associated with a product sequence is smaller than the threshold orunique scrambling sequences no longer remain available to form newproduct sequences.

If, upon completion of the successive iterations, no product sequenceleads to a PAPR that is smaller than the threshold, then the bufferedsequence after IDFT that leads to the smallest PAPR, albeit larger thanthe threshold, is selected for transmission.

In another aspect of the present invention, a scrambling sequence thatis combined with a data block in each iteration is selected from a setof scrambling sequences. Each scrambling sequence is independent fromother sequences. And, each scrambling sequence is of the lengthcorresponding to the length of the data block. The values of the binary,scrambling sequence are of randomly-generated “1” or minus “1” values.The scrambling sequences are, e.g., randomly generated off-line and inadvance, then saved at both the transmitting and receiving stations. Thereceiving station thereby knows the entire set of sequences in advance.

In another aspect of the present invention, a buffer is provided tobuffer values of sequences out of IDFT together with their associated,calculated PAPRs. In each iteration, if the sequence after IDFT exhibitsa PAPR that is larger than the threshold, the sequence after IDFT andits associated PAPR are buffered. In the event that all candidatescrambling sequences have been iterated and no sequence after IDFT is ofa PAPR that is smaller than the threshold, then a determination is madeof which of the buffered sequences exhibits the smallest PAPR. Thebuffered sequence that exhibits the smallest PAPR is selected fortransmission and is retrieved from the buffer and caused to becommunicated.

In the event that a first product sequence after IDFT exhibits a PAPRsmaller than the threshold, only a single product sequence is formed.And, iterations of product-sequence formations, IDFT operations, PAPRcalculations, and comparison operations are performed successively untila PAPR of a product sequence after IDFT is determined to be smaller thanthe threshold. That is to say, product sequences are only formed to theextent needed. Determination is made responsive to formation of eachsuccessive product sequence as to whether the product sequence afterIDFT exhibits a PAPR smaller than the threshold. Extra productsequences, i.e., product sequences that might not be needed are notformed. Through the transmission of transformed product sequences afterIDFT that exhibit acceptable, or smaller-available, PAPRs, improvedcommunication performance is obtained.

In these and other aspects, therefore, apparatus, and an associatedmethod, are provided for forming a transmit block formed of a datablock. The transmit block is for communication pursuant to an OFDMscheme. A combiner is configured to combine the data block with aselected, scrambling sequence to form a combination sequence. Thetransmitter is configured to transmit the transformed combinationsequence after IDFT when a PAPR associated with the combination sequenceafter IDFT is of a selected level.

Referring first, therefore to FIG. 1, portions of a radio communicationsystem, shown generally at 10, include a set of communication stations12 and 14, interconnected by way of a radio air interface, hererepresented by the segment 16. In the exemplary implementation, thecommunication system 10 forms an OFDM (Orthogonal Frequency DivisionMultiplexing)-based communication system, or other MCM (Multi-CarrierModulation)-based communication system. OFDM-based communication schemesare proposed for a so-called fourth generation (4G) cellularcommunication system. The following description shall describe exemplaryoperation with respect to implementation of the communication system asa 4G, OFDM-based cellular communication system. It should be understood,however, that the following description is analogously alsorepresentative of many other communication systems, both wireless andwireline, in which data blocks are communicated. Additionally,description of operation shall be described with respect to thecommunication station 12 forming a network station, and thecommunication station 14 forming a mobile station or vice versa. In theexemplary implementation, both the communication stations includeanalogous functionality and are operable in analogous manners.

A data source 22 sources data. Each data is a value taken from an M-arysignal constellation. And, each data block is formed of N such values ingeneral. A data block sourced at the data source is provided, hereindicated by way of the line 24, to a multiplier 28 that forms acombiner. The multiplier multiplies symbol values together with ascrambling sequence provided to the multiplier on the line 32. Thescrambling sequence is provided on the line 32 by a scrambling sequenceprovider 34. The scrambling sequence provider forms a sequence generatoror a cache of scrambling sequences, available for retrieval and use forcombination with the data block at the multiplier 28. Each scramblingsequence is a sequence of binary values with different binary sequencesforming independent sequences, each consisting of N numbers of randomlygenerated 1 and −1 values. The multiplier combines the data block andthe scrambling sequence to form a product sequence, viz., a combinationsequence. The sequence is provided, here indicated by way of the line38, to an IDFT (Inverse Discrete Fourier Transform) operator 42. TheIDFT operator performs an IDFT operation upon the combination sequenceon the line 38 and generates a transformed block of values on the line44.

The transformed block of values is provided to a PAPR (Peak to AveragePower Ratio) calculator 48. The PAPR calculator calculates a value ofthe PAPR for the transformed block of values thereto. And, thecalculated PAPR value, formed on the line 52, is provided to a thresholdcomparator 54. The threshold comparator compares the value of the PAPRcalculated by the calculator 48 with a pre-determined threshold value.If the calculated PAPR associated with the transformed block of valuesis smaller than the threshold, then a decision is made to send thetransformed values of the product sequence associated with theacceptable PAPR value. An indication of the scrambling sequence used inthe formation of the product sequence is provided to a control signalgenerator comprising a scrambling sequence ID provider 58.

The provider 58 generates a control signal that identifies thescrambling sequence used in the product sequence formation. The provider58, for instance, generates control bits that populate a field of acontrol signal that is sent by the communication station. The transmitchain includes a D/A (Digital-to-Analog) and an IF/RF (IntermediateFrequency/Radio Frequency) element 62. The control signal generated bythe control signal generator 58 is caused to be transmitted by theelement 62. When a value of the PAPR calculated by the calculator issmaller than the threshold, the threshold comparator permits theassociated product sequence after IDFT to be provided to the element 62to be transmitted therefrom. In the event that the PAPR value is largerthan the threshold, then the product sequence after IDFT and itsassociated PAPR value are buffered at a buffer 66. And, an indication isprovided, here indicated by the line 68 to the scrambling sequenceprovider 34 and to the multiplier 28 to indicate the negative results ofthe comparison made by the comparator.

Responsive to the notification of the negative results, a new iterationcommences. That is to say, a new scrambling sequence is provided by thescrambling sequence provider to the multiplier 28, and a newcombination, i.e., product, sequence is formed. The new product sequenceis transformed by the IDFT operator, its PAPR is calculated by thecalculator 48, and the threshold comparator compares the calculated PAPRvalue against the threshold. Responsive to the comparison, the newproduct sequence after IDFT is of a PAPR that is acceptable, or not. Ifacceptable, the control signal generator operates, and the productsequence after IDFT is caused by the element 62 to be transmitted.Otherwise, the product sequence after IDFT and its associated PAPR arebuffered at the buffer and additional iteration is performed, if aunique scrambling sequence remains to be provided.

If no more iterations with unique scrambling sequences can be performed,the threshold comparator accesses the buffer contents of the buffer 66and compares the PAPR values stored therein. The buffered sequenceassociated with the smallest of the buffered PAPR values is selected tobe sent by the communication station. Buffered information associatedwith the scrambling sequence used in the formation of the selectedproduct sequence is also retrieved and provided to the control signalgenerator 58. The control signal generator causes a control signal to besent by the communication station 12, to the receiving station, here thecommunication station 14, to alert the communication station 14 of thescrambling sequence used in the formation of the product sequence thatis to be communicated thereto.

Thereby, a data block is altered, through the combination with ascrambling sequence, to alter the PAPR to facilitate its communicationto the communication station 14. The operation is iterative such thatunneeded operations are not performed. That is to say, if the firstcombination sequence, i.e., product sequence, leads to an acceptablePAPR after IDFT, additional product sequences need not be formed. And,during any iteration, if a product sequence is formed of an acceptablePAPR after IDFT, additional product sequences are not formed. And, ifnone of the product sequences exhibits an acceptable PAPR, selection ismade of the product sequence associated with the smallest, albeitotherwise unacceptable, PAPR. And, by notifying the receivingcommunication system of the scrambling sequence that is used to form theproduct sequence, the receiving station is able, in its receive chainoperation, to recover the informational content of the data block.

FIG. 2 illustrates a process diagram shown generally at 82,representative of the process of operation of an embodiment of thepresent invention, such as that provided during operation of theapparatus 12, shown in FIG. 1. Then, and as indicated by the block 86, anew data set, X, is provided, in which q=1. Then, and as indicated bythe multiplier 88, the data set is multiplied with a scrambling sequenceB (q) provided by way of the path 92. A product sequence is formed andprovided, by way of the line 94, to the block 96 at which an IDFT isperformed upon the product sequence.

Then, and as indicated by the decision block 102, a determination ismade as to whether the PAPR associated with the transform of the productsequence is smaller than a threshold. If smaller than the threshold, the“smaller” branch is taken to the block 104, and the transformed productsequence is transmitted. If, conversely, the calculated PAPR is largerthan the threshold, a “larger” branch is taken to the decision block106. A determination is made, indicated by q less than L, as to whetheradditional scrambling sequences are available by which to be combinedwith the data block. If an additional scrambling sequence is available,the “yes” branch is taken to the block 108, and transformed sequence issaved, together with its associated PAPR. Selection of a new scramblingsequence is made at the block 112, indicated by the incrementing of thesmall letter q variable. Then, and as indicated by the block 114, a newscrambling sequence is obtained and provided, by way of the path 92, tothe multiplier 88 for a subsequent iteration of operation.

The subsequent iteration of operation is only carried out in the eventthat the earlier iteration fails to form a product sequence that leadsto an acceptable PAPR.

If, at the decision block 106, a determination is made that no morescrambling sequences is available, the “no” branch is taken to the block118 whereat selection of a transformed product sequence from amongstsaved sequences in prior iterations of the process is made. Selection ismade of the saved sequence that exhibits a best, i.e., the smallest,PAPR value.

Once selection is made, a path is taken to the block 104, and theselected, transformed sequence is transmitted.

Thereafter, a path is taken to the decision block 112, and adetermination is made as to whether additional symbols are available fortransmission. If so, the “yes” branch is taken back to the block 86.Otherwise, the “no” branch is taken to the stop block 124.

The collection of all data symbols X_(n), n=0,1, . . . , N−1, is denotedas a vector X=[X₀, X₁, . . . , X_(N−1)]^(T) that will be termed as adata block, where the superscript T stands for transposition, and X_(n)takes a value from an M-ary signal constellation. The complex basebandrepresentation of a multi-carrier signal consisting of N subcarriers isgiven by

$\begin{matrix}{{{x(t)} = {\frac{1}{\sqrt{N}}{\sum\limits_{k = 0}^{N - 1}{X_{n}{\exp \left( {j\; 2\; \pi \; {nf}_{\nabla}t} \right)}}}}},\mspace{11mu} {0 \leq t < {NT}}} & (1)\end{matrix}$

where j=√{square root over (−1)}, f_(∇), is the frequency spacingbetween adjacent subcarriers, and NT denotes the data block period. InOFDM the subcarriers are orthogonal

$\left( {{i.e.},{f_{\nabla} = \frac{1}{NT}}} \right).$

The transmitted RF signal is

s(t)=R _(e) {x(t)exp(j2πf _(c) t)}  (2)

where f_(c) is the carrier frequency, and R_(e){u(t)} stands for thereal part of u(t). The PAPR of the baseband signal is defined as

$\begin{matrix}{{PAPR} = \frac{\max\limits_{0 \leq t < {NT}}{{x(t)}}^{2}}{{1/{NT}} \cdot {\int_{0}^{NT}{{{x(t)}}^{2}\ {t}}}}} & (3)\end{matrix}$

An approximation in which only mN equidistant samples of x(t) areconsidered where m is an integer larger than or equal to 1. These“m-time oversampled” time-domain samples are represented as a vectorx=[x₀, x₁, . . . , x_(mN−1)]^(T) and obtained as

$\begin{matrix}{{x_{k} = {{x\left( {{kT}/m} \right)} = {\frac{1}{\sqrt{N}}{\sum\limits_{n = 0}^{N - 1}{x_{n}{\exp \left( {j\; 2\; \pi \; {knf}_{\nabla}{T/m}} \right)}}}}}},\mspace{14mu} {k = 0},1,\ldots \mspace{11mu},{{mN} - 1}} & (4)\end{matrix}$

The PAPR of the continuous-time signal cannot be obtained precisely byuse of the Nyquist rate sampling, which corresponds to the case of m=1.But, setting m=4 provides sufficiently accurate PAPR results. The PAPRcomputed from the m-time oversampled time domain signal samples is givenby

$\begin{matrix}{{PAPR} = {{\max\limits_{0 \leq k \leq {{mN} - 1}}r_{k}} = {\max\limits_{0 \leq k \leq {{mN} - 1}}\frac{{x_{k}}^{2}}{E\left\lbrack {x_{k}}^{2} \right\rbrack}}}} & (5)\end{matrix}$

where E[•] denotes expectation, and r_(k) is the normalized power ofx_(k). The sequence {x_(k)} in Eq.(4) is interpreted as the inversediscrete Fourier transform (IDFT) of the data block X with (m−1)N zeroespadded. As a sum of N independent random variables, in general, x_(k) isa complex random variable. A different data block of X usually yields adifferent sequence of {x_(k)} with a different PAPR.

As described above, binary scrambling sequences are used pursuant to anembodiment of the present invention. L binary scrambling sequences aredefined, denoted as B(q)=[[b₀(q),b₁,(q), . . . b_(N−1)(q)]^(T) with q=1,2, . . . , L, L a positive integer. For q=1, B(1) consists of all ones.For all other values of q>1, B(q)'s are independent sequences, eachconsisting of N numbers of randomly generated 1 or −1.

The process shown in FIG. 2 is also represented by the following fiveprimary operations:

(1) For each given sequence of X, start with q=1.

(2) Perform IDFT on the element-by-element product of X and B(q) to geta sequence {x_(k)}.

(3) Find out the PAPR of the sequence {x_(k)}. If the PAPR is below apredefined threshold, transmit {x_(k)} and claim success; otherwise save{x_(k)} (denoted as {x_(k)} (q)) and go to Step (4).

(4) If q<L, set q=q+1 and go back to Step (2); otherwise go to Step (5).

(5) Transmit the sequence x_(k) associated with the minimum PAPR amongthe L saved sequences of {x_(k)(q)}.

Each time when Step (2) is performed, X is multiplied with a new binarysequence B(q) to yield a new product sequence of {x_(k)(q)}, and in turnyield a different PAPR after IDFT. With a limited number of trials, aPAPR below, or closer to, the threshold is obtainable with a highprobability.

FIG. 3 illustrates a method block diagram, shown generally at 132,representative of the method of operation of an embodiment of thepresent invention. The method facilitates formation of a transmit blockformed of a data block. The transmit block is for communication pursuantto an OFDM, or other MCM, communication scheme.

First, and as indicated by the block 136, the data block is combinedwith a selected scrambling sequence to form a combination sequence.Then, and as indicated by the block 138, the combination sequence isselectably transmitted if a PAPR associated with the combinationsequence is smaller than a selected level.

Thereby, through appropriate selection of the scrambling sequence, adata block is better able to be communicated that leads to a smaller, oracceptable, PAPR level.

1. Apparatus for forming a transmit block formed of a data block, thetransmit block for communication pursuant to an OFDM scheme, saidapparatus comprising: a combiner configured to combine the data blockwith a selected scrambling sequence to form a combination sequence; atransmitter adapted selectably to receive the combination sequenceformed by said combiner, the combination sequence forming the transmitblock, said transmitter configured to transmit the combination sequenceforming the transmit block when a power ratio indicia associated withthe combination sequence is of a selected level.
 2. The apparatus ofclaim 1 further comprising a scrambling sequence provider configured toprovide the selected scrambling sequence to said combiner.
 3. Theapparatus of claim 2 wherein said scrambling sequence provider and saidcombiner are configured iteratively to provide successive scramblingsequences and successive combination sequences for a selected number ofiterations.
 4. The apparatus of claim 3 wherein the selected scramblingsequence combined by said combiner in each iteration by said combiner isindependent of others of the scrambling sequences.
 5. The apparatus ofclaim 3 further comprising a selector configured to select which of thesuccessive combination sequences formed pursuant to iterations thereofprovided by said combiner is to be transmitted by said transmitter. 6.The apparatus of claim 5 wherein said selector is configured to selectthe combination sequence that exhibits a power ratio indicia better thana selected threshold.
 7. The apparatus of claim 5 wherein said selectoris configured to select the combination sequence that exhibits a bestpower ratio indicia.
 8. The apparatus of claim 1 wherein the selectedscrambling sequence combined by said combiner with the data blockcomprises a binary sequence.
 9. The apparatus of claim 1 wherein thedata block is of a selected number of data symbols and wherein theselected scrambling sequence is of a sequence length at least of acorresponding selected number.
 10. The apparatus of claim 1 wherein thecombination sequence formed by said combiner is formed of a product ofthe data block and the combination sequence.
 11. The apparatus of claim1 wherein the power ratio indicia associated with the combinationsequence comprises a peak-to-average power ratio value.
 12. Theapparatus of claim 11, wherein said transmitter is configured selectablyto transmit the combination sequence if the peak-to-average power ratiovalue associated therewith is less than the selected level.
 13. Theapparatus of claim 1 further comprising a transformer configured toperform an inverse fast Fourier transform upon the combination sequence.14. A method for forming a transmit block formed of a data block, thetransmit block for communication pursuant to an OFDM scheme, said methodcomprising the operations of: combining the data block with a selectedscrambling sequence to form a combination sequence; and selectablytransmitting the combination sequence if a power ratio indiciaassociated with the combination sequence is of a selected level.
 15. Themethod of claim 14 further comprising the operation, prior to saidoperation of combining, of forming the selected scrambling sequence. 16.The method of claim 15 wherein said operations of forming and combiningare iteratively performed a selected number of iterations, forming aplurality of scrambling sequences and a plurality of combinationsequences.
 17. The method of claim 16 further comprising the operationof selecting which of the plurality of combination sequences to transmitduring said operation of selectably transmitting.
 18. The method ofclaim 17 wherein selection made during said operation of selecting is ofa combination sequence of the plurality of combination sequences thathas associated therewith a power ratio indicia of a best level.
 19. Themethod of claim 14 wherein the selected level of the power ratio indiciaassociated with the combination sequence is better than a selectedlevel.
 20. Apparatus for an MCM, Multicarrier Modulation, transmitter,said apparatus comprising: a combiner configured selectably to combinetogether a data block and at least a first scrambling sequence of a setscrambling sequences into a combined sequence; a selector configured toselect whether to permit transmission of the combined sequence formed bysaid combiner, selection made responsive to a power ratio indiciaassociated with the combined sequence.